Light sensitive diazo compound and binder composition



LIGHT SENSITIVE DIAZO COMPOUND AND BINDER COMPOSITION Martin Hephcr, Harrow,

Kodak Company, New Jersey England, assignor to Eastman Rochester, N. Y., a corporation of No Drawing. Application May 4, 1955 Serial No. 506,061

This invention relates to photographic processes for the production of layers which can be rendered ink accepting in an image-wise manner and use for lithographic and similar printing processes where greasy inks are employed.

It is well known to employ for lithographic and similar printing processes, a light-sensitive layer, such as a layer of gelatin impregnated with potassium bichromate, which is exposed to light and is then inked all over, followed by swabbing with water which removes the ink from the portions of the layer not hardened by the exposure to light. Many variations of this process have been proposed.

A difficulty in all such processes is that 'with sensitive layers which are sensitized with bichromate, it is necessary to perform the sensitization just prior to the exposure, which is often very inconvenient. The problem is to find a process which employs a sensitive layer which can be manufactured in a factory and will remain in good condition for use at later times, preferably days or weeks later and which can-then be processed in a simple manner to give a satisfactory printing surface.

I have now found that this problem can be solved by using certain azide sensitized layers of the kind hereinafter described, and incorporating in the colloidal material of the layer a quantity of either natural or synthetic rubber latex. Advantageously, the latex is mixed with the colloidal material before being coated as a sensitive layer. The incorporation of the latex increases the ink acceptance of the finally produced hardened image, and generally it is not necessary to apply further treatment to increase the hardness. Nevertheless, it is possible to impart extra physical hardness to the final image by treating it with a salt of a multi-valent metal. (For example, acidified potassium permanganate, acidified ammonium dichromate, chromic acid, zirconium sulfate, ferric chloride with hydrofluoric acid, copper-chloride, ferric oxalate, etc.)

Accordingly, it is an object of my invention to provide improved photographic layers containing azide compounds. Another object is to provide improved printing plates for lithographic, resist, and other related processes. Other objects will become apparent from a consideration of the following description and example.

The sensitive layers made according to the present invention may be coated on any suitable support. If coated on aluminum foil, then it is only necessary after exposure and washing to treat the image so produced with a suitable lithographic desensitizing solution to produce good hydrophilic qualities in the bare metal areas representing the non-printing parts. This can be carried out with the customary lithographic etching solutions, or for more permanent results, the acidified dichromate solutions known under the name of Cronak (J ernstcdt ASTM Bull. No. 137 (1945), pages 2935) and Brunak (Plate Surface Treatment (1950), Instruction Book No. 802 by Lithographic Technical Foundation, N. Y.

nited States Patent 2,848,328 Patented Aug. 19, 1958 16, N. Y) processes can be used. Also, good hydrophilic qualities can be produced on aluminum by depositing a zinc complex from a suitable aqueous solution.

Other suitable supports, such as glass, cellulose ester (e. g., acetate, acetate butyrate, etc.) film, polyvinyl acetal film, etc. can be employed in lieu of the abovementioned aluminum foil support. 'Other metal supports, e. g., magnesium, etc. can also be employed.

The azide compounds useful in practicing my invention are known as azidostyrylketones and azidostyry1- arylazides. These azide compounds can alvantageo-usly be represented by the following general formula:

wherein R represents a monocyclic arylene group of the benzene series (e. g., phenylene, methylphenylene, methoxyphenylene, etc.) and R represents an acyl group of a carboxylic acid (e. g., acetyl, propionyl, butyryl, benzoyl, toluoyl, carboxycarbonyl (COCOOH), azidobenzoyl, etc.) or an azidoaryl group of the benzene series (e. g., azidophenyl, azidotolyl, etc.), provided that said azide compound contains at least one substituent selected from the group consisting of a sulfo radical, a carboxyl radical, and alkali metal (e. g., sodium, potassium, etc.) salts of said radicals (the substituent or substituents being on the aryl nucleus or on the vinylene group). Cornpounds embraced by the above general formula which can be used in practicing my invention include the following, for example:

Disodium 4,4-diazidostilbene-2,2'-disu1fonate S OaNa I l z Sodium 3-azido-4-azidobenzalacetophenone-2-sulfonate O O Na Sodium 4,4'-diazidostllbene-a-carboxylate S OsNa Sodium di (4azido-2"hydroxybenza1)acetone-2-sulfonate 7 Sodium &1azidobenzalacetophenone-2-sulfonate Na CH=CHCCOOH 4-azido'benzalpyruvic acid Other aryl azide compounds,. not embraced by the above formula, can also be used in practicing my invention. Such aryl azide compounds include, for example:

Disodium 4,4-d iazidodiphenyl-3,3-disulf0nate Sodium 2- 4'-azidophenyl) -5-azid0-1,3-benzotriazo1e-6- sulfonate By natural rubber, I mean rubber which is commonly known as sulfur-vulcanizable. By synthetic rubber I mean polymers, and more particularly copolymers, of 1,3-diolefins, such as 1,3-butadiene, isoprene, neoprene, etc. Especially useful copolymers are those containing a minor (less than 50 percent by weight) proportion of unsaturated compound, such as isobutylene, styrene, acrylonitrile, etc. Such synthetic rubbers are known commercially as Buna S, Buna N, Butyl, etc. rubbers (OS). These rubbers, natural and synthetic, are employed in my invention in the form of an aqueous emulsion or dispersion (latex). The concentration of solids in the latex can be varied, although I have generally found that from about 40 to 70 percent by Weight of solids is convenient for the purposes of my invention.

Although it is preferred that the rubber latex be added to the aqueous coating solution of the colloid before coating, it is possible to obtain certain of the advantages of the invention if the colloid image not containing latex is bathed in a latex solution, either prior to or after the application of a desensitizing treatment. It is possible to vary the proportions of the latex solution to the colloid over a fairly wide range, usually from about 3 parts to about 120 parts (by weight) of latex solution to parts of the colloid (by weight). The preferred range is 5 to 100 parts of the latex solution to 5 parts of the colloid. The following example illustrates a suitable coating solution.

Example Parts by weight Casem 5 Disodium 4,4'-diazidostilbene-2,2-disulfonate 0.5 Ammonia (.880 gravity) 1.0 Water 100 To this was added:

Rubber latex dispersion (60% solids) 50 The coating was applied to a support in a thin layer by whirling at 300 R. P. M. When dry it was exposed in the usual manner in contact with a negative or positive image to the light from an arc, or mercury vapor source. Convenient exposure is 3 minutes at a distance of 18 inches from two 400 watt-high pressure mercury vapor lamps. After exposure the plate was rinsed in weak alkali for a few seconds, e. g., 2% sodium carbonate solution. (After rinsing it is possible to apply greasy lithographic ink to the stencil where it will adhere quite firmly.) On the other hand, it is usually desirable to make the bare metal areas more hydrophilic by treating in a phosphate or chromate solution. Excellent a results were obtained when the plate was bathed for 2 minutes in the following solution:

. Parts Ammonium dichromate 2 Hydrofluosilicic acid 0.3 Water After bathing in this solution the plate was rinsed and dried and then placed on the lithographic press, where inking took place immediately.

Most advantageously, the colloid to use with the azide and rubber latex dispersion is casein, but it has been found that any of the above water-soluble colloids containing aryl azides which are hardened on exposure to light also gain in their ink acceptance by the inclusion of the latex dispersion.

It has been noticed that in the coated layers the rubber appears to coagulate more at the outer surface, and it was found that if coatings containing a fairly high proportion of latex was used, then the rubber surface on the stencil could be coalesced to a thoroughly firm and continuous layer by briefly treating with a suitable solvent. It is, for instance, possible to rapidly wet the stencil with benzene and dry this by blowing with air so that a completely water-proof surface to the stencil is obtained.

The stencils produced according to the present inven tion are useful for other photomechanical applications, such as the production of relief images by sand blasting techniques, and provision of etching resists, or stencils for silk screen printing, etc.

What I claim as my invention and desire secured by Letters Patent of the United States is:

1. A light-sensitive coating composition comprising a mixture of (l) casein, (2) an aqueous dispersion of a latex selected from the group consisting of natural rubber latex and synthetic rubber latex, and (3) an aryl azide compound selected from those represented by the following general formula:

wherein R represents a monocyclic arylene group of the benzene series, R represents a member selected from the group consisting of a carboxylic acyl group and an azidoaryl group of the benzene series, provided that said aryl azide compound contains at least one substituent selected from the group consisting of a sulfo radical, a carboxyl radical, and alkali metal salts of said radicals, said composition being adapted to produce a lightsensitive coating in which an image can be formed by exposure to light and washing in an aqueous solution.

2. A light-sensitive coating composition comprising a mixture of 1) casein, (2) an aqueous dispersion of a latex selected from the group consisting of natural rubber latex and synthetic rubber latex, and (3) disodium 4,4'-diazidostilbene-2,2-disulfonate.

3. A light-sensitive photographic material comprising a support having thereon a mixture of (l) casein, (2) an aqueous dispersion of a latex selected from the group consisting of natural rubber latex and synthetic rubber latex, (3) an aryl azide compound selected from those represented by the following general formula:

wherein R represents a monocyclic arylene group of the benzene series, R represents a member selected from the group consisting of a carboxylic acyl group and an azidoaryl group of the benzene series, provided that said aryl azide compound contains at least one substituent selected from the group consisting of a sulfo radical, a carboxyl radical, and alkali metal salts of said radicals, said material being adapted to produce a photographic image upon exposure to light and washing in an aqueous solution.

4. A light-sensitive photographic material comprising a support having thereon a mixture of (l) casein, (2) an aqueous dispersion of a latex selected from the group consisting of natural rubber latex and synthetic rubber latex, and (3) disodium 4,4'-diazidostilbene-2,2'-disu1- fonate, said material being adapted to produce a photographic image upon exposure to light and washing in an aqueous solution.

References Cited in the file of this patent UNITED STATES PATENTS Staehle Dec. 12, 1950 Staehle July 22, 1952 Staehle Apr. 13, 1954 Neugebauer Apr. 13, 1954 Neugebauer Oct. 26, 1954 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 2,848,328 August 19, 1958 Martin Hepher Column 3, line 16, for "752,582" read 752,852 a Signed and sealed this 4th day of November 1958 (SEAL) Atfiest:

KARL Ho AJQINE ROBERT C. WATSON Attesting Officer Commissioner of Patents 

1. A LIGHT-SENSITIVE COATING COMPOSITION COMPRISING A MIXTURE OF (1) CASEIN, (2) AN AQUEOUS DISPERSION OF A LATEX SELECTED FROM THE GROUP CONSISTING OF NATURAL RUBBER LATEX AND SYNTHETIC RUBBER LATEX, AND (3) AN ARYL AZIDE COMPOUND SELECTED FROM THOSE REPRESENTED BY THE FOLLOWING GENERAL FORMULA: 